This experiment was conducted in 2010 and 2011 to investigate the effect of defoliation timing on yield, quality traits and storage capability of tuber in potato crop. The experiment was carried out as factorial arrangement in randomized complete blocks design with two factors and three replications. Experimental factors comprised defoliation timing at five levels; complete removal of haulm in 7, 14, 21 and 28 days before physiological maturity phase of potato crop and control treatment haulms were not removed Second factor was two cultivars of potato, “Agria” and “Savalan”. Tubers were harvested in two weeks after defoliation in all treatments. Total tuber yield, number of tuber in different sizes (large, seed and small tuber) were weighed and counted. Some quality characteristics of tuber such as dormancy longevity, dry matter percentage, reduced sugar of tuber and amount of vitamin C were also measured. Mean comparisons showed that highest yield and large tuber were achieved in control (not defoliated) followed by defoliated 7 days before physiological maturity phase as they were not significantly different. These two treatments produced higher total yield (35.8 and 34.3 ton.ha-1, respectively), but were not significantly different from defoliated treatment 14 days before physiological maturity. In term of seed size tuber, the highest amount (14.44 number.m-2) was counted in defoliated 14 days before physiological maturity. Defoliation in 7 and 14 days before physiological maturity phase produced higher amount of vitamin C (50.23 and 48.35 mg.100g-1Fw, respectively), and were not significantly different from control. The highest amount of reduced sugar (3.04 mg.100g-1Fw) achieved in defoliation 28 days before physiological maturity phase. The tubers produced in defoliation in 7 and 14 days before physiological maturity phase as well as control had longer tuber dormancy. In conclusion, defoliation in 7 and 14 days before physiological maturity phase were superior treatments in respect with total yield and seed tuber size as well as other quantitative and qualitative characteristics of tuber. Therefore, these two defoliation timing can be recommended for seed tuber potato production.